1. Field of the Invention
The present invention relates to a method for providing an operator with visual information for guiding the position and orientation of images or a probe in three-dimensional space.
2. Description of the Prior Art
The inventor has discovered a need for a method, using the apparatus described in U.S. Pat. No. Re. 30397 for allowing an operator to accurately position and display the position and orientation of an image or non-imaging probe in three-dimensional space, with particular regard to the orthogonal, "non-visualized" dimension not seen in the conventional two-dimensional image.
This method is useful in medical diagnosis. For example, it provides a reliable and effective means for making more accurate and reproducible measurements of the heart by use of ultrasound imaging.
Ultrasound images are two-dimensional, cross-sectional, tomographic images, A general characteristic of conventional two-dimensional, real-time ultrasound scanners is that they have no means for spatial registration of the position and orientation of the scanning transducer and its image with respect to an independent spatial coordinate system. Conventional two-dimensional, real-time ultrasound scanners can be moved, angulated and rotated into an almost infinite variety of positions and orientations. Because the scanning transducer is hand-held by the operator, the position and orientation of images is guided by the proprioceptive sense of the operator as he/she interprets image content in terms of a prior knowledge of anatomy. The only visual indication to the operator of spatial dimensions that he/she is able to use is that given in the two-dimensional image itself. He/she has no visible knowledge of the position and orientation of the image with respect to internal anatomic landmarks in the third dimension not visualized in the image. This lack of visible orienting information is a major problem to conventional ultrasound imaging because the scanning transducer must be deliberately positioned and its image acquired by the operator.
When the variety of potential positions and orientations of the image is coupled with the variation found in normal anatomy a serious problem exists of accurately locating and documenting the position of an image. In current practice there is significant uncertainty concerning the exact position and orientation of the image. This problem has represented an important difficulty in the conventional use of diagnostic ultrasound imaging requiring a high degree of operator skill. The uncertainty of position and orientation and its consequent variability, as well as the operator skill required to deal with this problem, has therefore limited the application and usefulness of ultrasound imaging.
This problem persists with use of the three-dimensional ultrasonic imaging apparatus as described in U.S. Pat No. Re. 30397. Although that apparatus registers image position and orientation in a three-dimensional spatial coordinate system there has been no means to convey this information to the operator of the system so that he/she may use it to guide operation of the system.
An important need of medical diagnosis using ultrasonic imaging is to make accurate and reproducible measurements of various organs. For example, when imaging the heart it is of great value to measure the size of chambers to determine the efficiency of cardiac pump function. To make such measurements accurate and reproducible, two requirements must be met. First, images must be obtained in a specified and reproducible position and orientation, and second, measurements within those images must be performed in a standardized manner. Because of the lack of registration of the movement of the ultrasound transducer and the lack of a means for displaying its position and orientation in the non-visualized dimension the former requirement is subject to systematic as well as random error. When these errors occur, erroneous measurements will result regardless of the performance of measurements within the image in a standardized manner. To be able to eliminate these errors, first, the movement of the transducer must be registered in three-dimensional space and second, a means to visually display image position and orientation in the orthogonal, "non-visualized" dimension must be found. The visual display of the relationship of the real-time image to anatomic landmarks in its non-visualized dimension will then feed back the information necessary for the operator to accurately position the real-time, two-dimensional ultrasound image.
The apparatus described in U.S. Pat. No. Re. 30397 provides a means for the spatial registration of the ultrasound transducer and image. Its use without additional refinement however does not provide the visual display necessary for accurate positioning of images. It is the purpose of this disclosure to describe a method to be followed that provides a means for accurately positioning an image with respect to translation, angulation and rotation in the dimensions not visualized in the image itself.
Use of the apparatus described in U.S. Pat. No. Re. 30397 without a visual display for image position has been made by Moritz et al. (Moritz et al. Computer-Generated Three-Dimensional Ventricular Imaging from a Series of Two-Dimensional Ultrasonic Scans. AM Rev. Diagnostics 1983; 3:73-77) for the purpose of imaging the ventricles of the heart and computing their volumes. They were presented with the problem of accurate positioning of image planes. They addressed it by recording a large number of intersecting images in a variety of positions and orientations hoping to adequately define all boundaries without the use of a visual display to guide image positioning. Brinkley et al. (Brinkley JF et al. Fetal Weight Estimation from Lengths and Volumes Found by Three-Dimensional Ultrasonic Measurements. J Ultrasound Med 1984; 3:162) used a similar system and algorithm for defining boundaries for the purpose of measuring fetal volume. They noted the deficiency of this approach, particularly for defining end-planes. Levine et al. (Levine RA et al. Three-Dimensional Echocardiographic Reconstruction of the Mitral Valve, with Implications for the Diagnosis of Mitral Valve Prolapse. Circulation 1989; 80:589) also used the system described in U.S. Pat. No. Re 30397 for the purpose of reconstructing the three-dimensional anatomic relationships of the mitral valve. They did not address the problem of a visual means for guiding image plane positioning. Other three-dimensional scanners utilizing mechanical apparatus for position registration (Raichlen JS et al. Dynamic Three-Dimensional Reconstructions of the Left Ventrical from Two-Dimensional Echocardiograms. J Am Coll Cardiol 1986; 8:364) have been constructed but none has addressed the problem of image positioning in the non-visualized dimension. Three-dimensional reconstruction of the heart by means of transesophageal echocardiography (Martin RW et al. Measurement of Stroke Volume with Three-Dimensional Transesophageal Ultrasonic Scanning: Comparison with Thermodilution Measurement Anesthesiology 1989; 70:470) has also been attempted without the use of an image positioning guidance method other than that used with conventional system. In summary, none of the three-dimensional ultrasound imaging systems developed to date, including some based on the apparatus described in U.S. Pat. No. Re 30397, have provided a means to prospectively and interactively guide image positioning by the operator or to document visually image position and orientation in the examination record.